This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Actin assembly and disassembly are thought to be key components of the machinery that drives motility at the cell leading edge. Many of the key regulatory molecules have been identified and their interactions have been quantitated. This makes this system ideal for modeling and simulation. However, it is not clear if all of the players are truly known, so a model can aid in establishing whether the system is sufficiently determined to be able to explain the overall system behavior. Virtual cell is an ideal platrform for building a hierarchical set of models that can capture the complexity of the system in an orderly progression and with direct reference to validating experiments. This problem will drive the technological development of Virtual Cell toward being able to properly represent and simulate polymerization.